Solvent-Free, Open-Vessel Microwave-Promoted Heck Couplings: From the mmol to the mol Scale

Nicholas E. Leadbeater; Victoria A. Williams; Thomas M. Barnard; Michael J. Collins Jr

doi:10.1055/s-2006-951512

LETTER

Solvent-Free, Open-Vessel Microwave-Promoted Heck Couplings: From the mmol to the mol Scale

Nicholas E. Leadbeater*^a, Victoria A. Williams^a, Thomas M. Barnard^b, Michael J. Collins Jr.^b
^a Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs, CT 06269-3060, USA
Fax: +1(860)4862981; e-Mail: nicholas.leadbeater@uconn.edu;
^b CEM Microwave Technology, 3100 Smith Farm Road, Matthews, NC 28104, USA

Abstract

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Abstract

The rapid, microwave-promoted Heck coupling of aryl iodides in open reaction vessels is presented and scale-up of the reactions to the mol scale demonstrated. Reactions are performed using 0.1 mol% palladium acetate as the catalyst, sodium carbonate and tributylamine as bases and tetrabutylammonium bromide as an additive.

Key words

palladium - Heck reaction - catalysis - solvent-free - microwave

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Referenzen

References and Notes

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It is more appropriate to call the Pd(OAc)₂ a precatalyst since a colloidal palladium species is most likely the catalytically active species.

It is important that a suitably sized reaction vessel is used for scale-up reactions in the absence of solvent. It is advised that the contents should occupy no more than 10% of the vessel volume. In addition, microwave power should be carefully modulated. A power no greater than 600 W is advised.

At a first glance it may seem that this would be putting in much more microwave power than in the case of the monomode experiments. However, the relative size of the cavity needs to be considered. Multimode microwaves have large cavities and so power is dissipated over a large area. Monomode equipment has a much smaller cavity and the energy density is up to some 30-40 times higher than the multimode apparatus.